The invention relates to a projection exposure apparatus for microlithography comprising a plurality of optical components forming an exposure beam path. Furthermore, the projection exposure apparatus comprises a distance measurement system. The invention furthermore relates to a method for distance measurement in a projection exposure apparatus for microlithography.
Highly productive projection exposure apparatus for microlithography react sensitively to vibration excitations, such as are produced during the scanning movement of reticle and wafer. Such vibration excitations lead to deflections of the optical components of the projection exposure apparatus with regard to the desired position thereof in the beam path, which leads to imaging aberrations. In accordance with one approach for minimizing these effects, the optical components are continuously measured with regard to their position. With regard to measured deflections, corresponding correction measures are implemented. Dynamic sensors on a capacitive basis or in the form of moving coils are envisaged for position measurement. Such sensors, in a manner governed by the design, have to be positioned very close to the area to be measured, which can cause drift, for example thermal drift, and impairs the measurement accuracy of the sensor. Moreover, these sensors can in turn have a disadvantageous effect on the dynamic behavior of the optical components.